A novel hepatitis B virus subgenotype, D7, in Tunisian blood donors

Tunisia is a medium-level epidemic country for hepatitis B virus (HBV). This study characterizes, for the first time, full genome HBV strains from Tunisia. Viral load quantification and phylogenetic analyses of full genome or pre-S/S sequences were performed on 196 hepatitis B surface antigen (HBsAg)-positive plasma samples from Tunisian blood donors. The median viral load was 64.65 IU ml(-1) (range<5-7.7x10(8) IU ml(-1)) and 89% of samples had viral loads below 10,000 IU ml(-1). Fifty-nine strains formed a novel subgenotype D7, 41 strains clustered in subgenotype D1, seven strains in subgenotype A2 and one strain in genotype C. The novel subgenotype D7 was defined by maximum Bayesian posterior probability, a genetic divergence from other HBV/D subgenotypes by >4% and a stronger HBV/E signal in the X to core genes than subgenotype D1. In conclusion, HBV/D is dominant in asymptomatic Tunisian HBsAg carriers and a novel subgenotype, D7, was the most common subgenotype found in this population.